The present invention relates to a probe method and apparatus for inspecting the electrical characteristics of an object to be inspected and, more particularly, to a probe method and apparatus for inspecting the electrical characteristics of an inspection item of an object to be inspected at a predetermined temperature.
A typical example of an inspection item of an object to be inspected includes integrated circuits (to be referred to as chips hereinafter) formed on a silicon wafer (to be referred to as a wafer W hereinafter). The inspection item of the present invention is not limited to the chips but also includes any electronic appliances and components the electrical characteristics of which can be inspected by so-called probing.
FIG. 14 shows an example of a conventional probe apparatus 10. Referring to FIG. 14, each object to be inspected (to be referred to as a wafer W hereinafter) stored in a cassette C in a loader chamber 11 is conveyed to a prober chamber 12 that inspects the wafer W. The prober chamber 12 and loader chamber 11 are controlled by a controller 13. A display 14 also serves as an operation panel for controlling the controller 13.
A wafer convey mechanism 15 and a sub chuck 16 are disposed in the loader chamber 11. While the wafer convey mechanism 15 conveys the wafer W from the cassette C to the prober chamber 12, the wafer W is pre-aligned by the sub chuck 16 with reference to its orientation flat. A wafer recognition mechanism (not shown) using a bar code reader, an OCR, and the like is arranged in the loader chamber 11. This wafer recognition mechanism reads a bar code or character information indicated on part of the wafer W.
A main chuck 20 on which the wafer W is placed and controlled to a predetermined temperature is arranged in the prober chamber 12. The main chuck 20 can be moved in the X, Y, Z, and .theta. directions by an X-Y (stage) moving mechanism 18, an elevating mechanism (not shown), and the like. A probe card 22, the main chuck 20, and an alignment mechanism 21 are placed in the prober chamber 12. The probe card 22 has probes or probe needles for electrically inspecting the wafer W. The alignment mechanism 21 accurately aligns the wafer W placed on the main chuck 20 with the probes. For example, the alignment mechanism 21 has a lower CCD camera 21D for image recognition, an alignment bridge 21B on which an upper CCD camera 21A is set to face downward, and a pair of guide rails 21C for reciprocally moving the alignment bridge 21B in the Y direction. Although FIG. 14 shows only the upper CCD camera 21A and does not show the lower CCD camera 21D, the lower CCD camera 21D is mounted on, e.g., the main chuck.
When inspecting wafers W, the wafer convey mechanism 15 extracts one wafer W from the cassette C in the loader chamber 11. While being conveyed by the wafer convey mechanism 15 toward the main chuck 20, the wafer W is pre-aligned by the sub chuck 16. Along with this, as shown in FIG. 12A, a plurality of probes or probe needles 22A are aligned by the alignment mechanism 21 and main chuck 20. After that, the alignment bridge 21B moves to the probe center and the main chuck 20 moves in the X, Y, and Z directions, to obtain a reference position in the prober chamber 12 by using the upper and lower CCD cameras 21A and 21D and a target 21E which is provided to the main chuck 20 and can move forward/backward, as shown in FIG. 12B. Then, the wafer convey mechanism 15 transfers the wafer W from the loader chamber 11 onto the main chuck 20 in the prober chamber 12. The main chuck 20 moves in the X, Y, and .theta. directions, as shown in FIG. 12C, to align the wafer W by using the CCD camera 21A. The main chuck 20 moves to move a chip, which is to be inspected first, to immediately under the probe card 22. The main chuck 20 moves upward in the Z direction from the current position to bring the probes 22A and the electrode pads of the chip into contact with each other. With the main chuck 20 over-driven, inspection of the electrical characteristics of the wafer W is started.
The probe card 22 is fixed in the opening at the center of a head plate through an insert ring. The head plate is arranged on the upper surface of the prober chamber 12 and can be opened/closed. A test head (not shown) is movably disposed on the upper surface of the prober chamber 12. The test head electrically connects the probes of the probe card 22 and a tester (not shown) with each other, and receives a predetermined signal from the tester and transmits it to the electrodes of the chip formed on the wafer W through the probes. The electrical characteristics of the chip are sequentially inspected by the tester.
To inspect the electrical characteristics of the chip at a high temperature of, e.g., 180.degree. C., the main chuck 20 and the wafer W are heated to a predetermined high temperature by a heating mechanism in the main chuck 20. The electrode pads of the chip and the probes are brought into electrical contact with each other to inspect the electrical characteristics of the chip. To inspect the electrical characteristics of the wafer W at a low temperature of, e.g., -50.degree. C., the main chuck 20 and the wafer W are cooled to a predetermined low temperature by a cooling mechanism in the main chuck 20. The electrode pads of the chip and the probes are brought into electrical contact with each other to inspect the electrical characteristics of the chip. In the case of low-temperature inspection as well, the chip is cooled to a predetermined low temperature, in the same manner as in high-temperature inspection, and its electrical characteristics are inspected.
Following alignment of the electrode pads formed on the wafer W and the probes of the probe card 22 with each other, when inspection is to be performed at a high temperature of, e.g., 180.degree. C., the probe card 22 is gradually heated by radiation heat from the main chuck 20 and thermally expands. Then, the coordinate positions of the probes on the probe card 22 gradually deviate from the coordinate positions obtained in pre-alignment. In the case of low-temperature inspection, the probe card shrinks due to the low temperature, and its coordinate position also deviates.
FIG. 13 shows an example of misalignment (positional displacement) of the probe in the Z direction in the high-temperature inspection. In FIG. 13, the distal end of the probe shifts upward in the Z direction for several hours since the start of measurement. The probes and the electrode pads of the inspection item cannot accordingly come into correct contact with each other, but misalignment or needle-pressure abnormality occurs in the probe to degrade the inspection reliability. This misalignment of the distal end of the probe occurs not only in high-temperature inspection but also in low-temperature inspection. Furthermore, this positional displacement occurs while the probe card 22 and the probes reach a predetermined inspection temperature, e.g., when measurement is to be newly started and when interrupted measurement is to be resumed.
In the era of 12-inch wafers to come, not only the wafer size will increase but also the chip pattern will shrink and the pitch among the electrode pads of the chip will decrease. When a plurality of (e.g., 32) chips are to be inspected simultaneously, the size of the probe card increases and also the number of probes increases to decrease the pitch among the probes, making the thermal influence described above more and more conspicuous. For this reason, the probe card must be preheated before inspection to prevent thermal influence as much as possible. A considerable amount of time is required for this preheating, leading to a great decrease in throughput.
During inspection, sometimes inspection is interrupted and the main chuck is separated from the inspection position. For example, needle marks are checked or tips of the probes are polished in the course of inspection. In this case, since the main chuck 20 is separated from the over-driven position described above, the temperature of the probe card and probes drops gradually. When inspection is resumed, the positions of the probes gradually deviate from the coordinate positions obtained during probe alignment, as described above. In order to avoid this misalignment, if the probe card and probes are preheated manually as required, the throughput suffers greatly.